1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to interpolation process of image.
2. Related Background Art
For obtaining a still image, there have been proposed following various methods, for example.
At first there is conceived a method of writing the image signal of one frame into a memory land reading the image signal of such frame to obtain a still image. However, this method requires a memory of one frame capacity, and the image becomes blurred in case the image shows a motion between two fields constituting the frame.
There is also known a method of writing the image signal of one field into a memory and obtaining the still image of a frame by employing, for one field of the frame, the image signal stored in the memory and, for the other field, interpolating the signal of a line by adopting the image signal of an immediately upper or lower line.
In this method, there is only required the memory capacity of one field and there is no image blur resulting from the motion between the fields. However, though there is obtained an image of one frame in appearance, the resolution in the vertical direction is inferior to that in the above-mentioned method utilizing the frame memory, because two consecutive lines are constituted by a same image signal.
For this reason there is conceived a method of writing the image signal of one frame into a memory and outputting such image signal for example for the first field while, for the second field, detecting the motion between a pixel and the upper and lower lines and selecting either the image signal of the second field or a synthesized image signal according to the detected motion.
More specifically, in the absence of motion, the image signal of the second field is read from the memory and is outputted, but, in the presence of motion, the image signal of a pixel in the second field is interpolated by the image signals of upper and lower nearby pixels of the first field for output.
This method allows to prevent the loss in the vertical resolution and the image blur resulting from the motion between the fields.
However, in case of switching the image of the second field and the interpolated image according to the motion as explained above, there are required image signals of vertically consecutive three pixels for the purpose of motion detection.
For this purpose there is required a memory capable of access at a triple speed, but such high-speed memory is expensive.
Though the motion can also be detected without using such expensive memory, there is required memories of at least two lines, leading to a larger magnitude of circuitry.
There is already known a digital video tape recorder (VTR) capable of recording and reproducing the image signal in a state of digital signal.
Such digital VTR has various functions such as still image reproduction, and, in the following, there will be explained the slow reproduction at a xc2xd speed among such functions.
In such case, the image signal is reproduced by transporting the magnetic tape at a speed equal to xc2xd of that at the recording, so that the same image signal is reproduced twice in repetition. Therefore a slow reproduction image of a xc2xd speed is obtained by storing the reproduced image signal in a memory and reading the image signal of a same frame twice in repetition from the memory.
As the ordinary CRT monitor displays the image of one frame in the state of interlaced images of two fields, the image output from the VTR to the monitor is usually made with conversion into interlaced format.
Therefore, in the aforementioned slow reproduction, if an interlaced conversion process is applied as in the ordinary reproduction, there is obtained an output image as shown in FIG. 19. In this case, after the output of a second field f2 of the frame FR1 as the slow reproduction image, there is outputted a first field f1 of the frame FR1. Consequently the lapse of time in the reproduced image becomes discontinuous so that the reproduced image becomes unnatural.
Such discontinuity in the lapse of time in the reproduced image can be resolved by adopting an order of image reading from the memory as shown in FIG. 20 or 21. More specifically, in the example shown in FIG. 20, the first field f1 alone is outputted in each frame, while, in the example shown in FIG. 21, the first field f1 is outputted twice in repetition and then the second field f2 is outputted twice in repetition for each frame.
In the examples shown in FIGS. 20 and 21, however, the image of one frame is constituted by the either field only, so that the resolution of the reproduced image becomes xc2xd in comparison with the ordinary reproduction, and a diagonal line in the image cannot be displayed in smooth manner.
An object of the present invention is to solve the drawbacks mentioned above.
Another object of the present invention is to obtain an interpolated image of high definition without increasing the magnitude of circuitry.
Still another object of the present invention is to obtain a reproduced image of high definition, in reproducing the image from a recording medium.
The above-mentioned objects can be attained, according to an embodiment of the present invention, by an image processing apparatus comprising:
input means for entering an image signal of which one frame is composed of plural interlaced fields, each of which is divided into plural blocks each consisting of plural pixels; and
interpolation means for interpolating, among the image signal outputted from the input means in the unit of a block, the image signal of a second field, utilizing the image signal of a first field to output the image signal on the block unit basis.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following detailed description of the embodiments, to be taken in conjunction with the attached drawings.